1. Field of the Invention
This invention relates to a liquid crystal display device using a LED backlight and, more particularly, to a relatively large size, thin liquid crystal display device with reduced power consumption used in a television set and the like.
2. Description of the Related Art
A liquid crystal display device includes a TFT substrate on which pixel electrodes, TFTs (Thin Film Transistors) and the like are arranged in a matrix form, an opposite substrate which faces the TFT substrate and on which color filters and the like are arranged corresponding to the pixel electrodes on the TFT substrate, and liquid crystal which is sandwiched between the TFT substrate and the opposite substrate. The liquid crystal display device controls the light transmittance through the liquid crystal molecules on a pixel-by-pixel basis to generate an image.
The liquid crystal display device is employed in various fields for the reason that it can provide a reduction in thickness and weight. Because the liquid crystal itself does not emit light, a backlight is placed on the rear surface of the liquid crystal display panel. A liquid crystal display device with a relatively large size screen such as a television set employs a fluorescent tube as a backlight. However, LEDs (Light Emitting Diodes) have been increasingly employed in response to requests for a further reduction in thickness of a liquid crystal display device, an increase in a color reproduction range, and the like.
The backlight is divided into two types according to the position of a light source, namely a direct-lit backlight having a light source disposed directly under the liquid crystal display panel and an edge-lit backlight having a light source disposed on a side edge of a light guide plate. In many cases, a liquid crystal display device with a relatively large size screen employs a direct-lit backlight with a light source disposed directly under the liquid crystal display panel, in order to increase the brightness of the screen.
A related-art CRT television set or the like delivers a uniform brightness of the screen. However, in a television set or the like using the liquid crystal display device, the brightness of the screen is not necessarily required to be uniform, and the luminance may be set smaller in a peripheral area of the screen than that in a central area. WO2004/038283 discloses a structure of a direct-lit backlight using a fluorescent tube as a light source in which the dot patterns are respectively printed at different dot densities between central and peripheral portions of the reflecting surface such that the brightness level of the central area of the screen is lower than that of the peripheral area of the screen. WO2004/038283 also describes a structure of a direct-lit backlight using LEDs as light sources in which the density of the LEDs is varied depending on location in order to adjust the brightness of the screen.
JP-A No. 2002-75038 describes a structure of a relatively small size liquid crystal display device using an edge-lit backlight in which LEDs are arranged on a side edge of a light guide plate such that the LED density is varied between portions close to the center and close to an end of the side edge in order to adjust the luminance of the screen.
JP-A No. 2001-93321 describes a structure of a light guide plate of an edge-lit backlight in which plural light guide plates are seamlessly arranged in a first direction. The light guide plate described in JP-A No. 2001-93321 is a single light guide plate extending in a second direction perpendicular to the first direction.